Lubricating compositions for preventing or reducing pre-ignition in an engine

ABSTRACT

Disclosed is a lubricating composition including at least one base oil and at least one organomolybdenum compound selected from the molybdenum dithiophosphate compounds or the sulphur-free molybdenum complexes, for preventing or reducing pre-ignition in an engine, preferably in a vehicle engine.

The invention relates to the use of a lubricating composition for preventing or reducing pre-ignition in an engine. More particularly, the invention relates to the use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for preventing or reducing pre-ignition in an engine, preferably in a vehicle engine, in particular of a motor vehicle.

The present invention also relates to a method for preventing or reducing pre-ignition in an engine, preferably in a vehicle engine, especially of a motor vehicle, implementing this lubricating composition.

The present invention also relates to the use of an organomolybdenum compound in a lubricating composition for preventing or reducing pre-ignition in an engine, preferably in a vehicle engine, especially of automobiles.

Technological Background

Under ideal conditions, normal combustion in a spark-ignition engine occurs when a mixture of fuel, and in particular fuel and air, is ignited in the combustion chamber inside the cylinder by the production of a spark emanating from a spark plug. Such normal combustion is generally characterized by the expansion of the flame front through the combustion chamber in an orderly and controlled manner.

However, in some cases, the air/fuel mixture may be prematurely ignited by an ignition source prior to ignition by the spark of the spark plug, resulting in a phenomenon known as pre-ignition. It is preferable to reduce or even eliminate pre-ignition, as this generally results in the presence of a sharp increase in temperatures and pressures in the combustion chamber, and may thus lead to a significant negative impact on the efficiency and the overall performance of an engine. In addition, pre-ignition may cause significant damage to the cylinders, pistons, spark plugs and valves in the engine and in some cases may even lead to engine failure or even engine damage. Recently, Low Speed Pre-Ignition (LSPI) has been identified, particularly by car manufacturers, as a potential problem for small engines (or downsized engines). LSPI typically occurs at low speeds and high loads, and may cause serious damage to pistons and/or cylinders.

Thus it would be desirable to have a lubricant that may prevent or reduce the risk of pre-ignition, including LSPI.

Solutions for decreasing the calcium content or increasing the zinc dithiophosphate or molybdenum dithiocarbamate content in a lubricant have been described (Takeuchi et al, “Investigation of Engine Oil Effect on Abnormal Combustion in Turbocharged Direct Injection—Spark Ignition Engines,” SAE Int. J. Fuels Lubr. 5 (3): 1017-1024, 2012 Hirano et al, “Investigation of Engine Oil Effect Abnormal Combustion in Turbocharged Direct Injection—Spark Ignition Engines (Part 2),” SAE Technical Paper 2013-01-2569, 2013). However, these solutions remain still insufficient to significantly reduce pre-ignition and are difficult to implement, especially in countries where a high level of basicity is required in fuels. In addition, problems of lubricant stability or compatibility with post-treatment systems are associated with these solutions.

WO2015023559 discloses a method for reducing pre-ignition by adding, in a lubricating composition, an additive for retarding ignition, wherein the additive is selected from among organic compounds comprising at least one aromatic ring. However, these light organic compounds could cause an excessive increase in lubricant volatility.

An object of the present invention is, therefore, to provide compounds and a lubricating composition comprising these compounds to overcome all or part of the aforementioned drawbacks.

Another object of the present invention is to provide a lubricating composition for preventing or reducing pre-ignition in an engine and whose formulation is easy to implement.

Another object of the present invention is to provide a lubricating composition for preventing or reducing pre-ignition in an engine while maintaining satisfactory or improved lubrication properties.

Another object of the present invention is to provide a lubrication method for preventing or reducing pre-ignition in an engine.

SUMMARY OF THE INVENTION

The invention thus relates to the use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for preventing or reducing pre-ignition in an engine, wherein the organomolybdenum compound is chosen from among:

-   -   molybdenum dithiophosphate compounds (Mo-DTP), or     -   molybdenum complexes free from sulfur.

Surprisingly, the Applicant has found that the presence of at least one organomolybdenum compound chosen from among the Mo-DTP and sulfur-free molybdenum complexes in a lubricating composition enables the lubricating composition, once implemented in an engine, to prevent or reduce pre-ignition in the engine.

Thus, the present invention makes it possible to formulate lubricating compositions providing both good stability and good pre-ignition prevention or reduction properties when used in an engine.

Advantageously, the lubricating compositions according to the invention have good pre-ignition prevention or reduction properties once they are implemented in an engine without the need to associate them with other technical solutions to prevent or reduce pre-ignition, and in particular technical solutions requiring the reduction of the calcium or magnesium content or causing an excessive increase in the volatility of the lubricating composition.

Advantageously, the lubricating compositions according to the invention have good properties for the prevention or reduction of pre-ignition when implemented in an engine, and whose formulation is easy to implement.

In one embodiment according to the invention, the organomolybdenum compound is a sulfur-free molybdenum complex selected from among organic molybdenum complexes with amide ligands and prepared by reaction of a molybdenum source and a derivative of amino, and of fatty acids preferably comprising from 4 to 28 carbon atoms, more preferably from 8 to 18 carbon atoms.

In another embodiment according to the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising at least one compound chosen from among:

-   -   the compounds of formula (A)

-   -   in which     -   X¹ represents an oxygen atom or a nitrogen atom;     -   X² represents an oxygen atom or a nitrogen atom;     -   n represents 1 when X¹ represents an oxygen atom and m         represents 1 when X² represents an oxygen atom;     -   n represents 2 when X¹ represents a nitrogen atom and m         represents 2 when X² represents a nitrogen atom;     -   R¹ represents a linear or branched, saturated or unsaturated         alkyl group comprising from 3 to 30 carbon atoms, preferably         from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon         atoms;     -   the compounds of formula (B)

-   -   in which     -   X¹ represents an oxygen atom or a nitrogen atom;     -   X² represents an oxygen atom or a nitrogen atom;     -   n represents 1 when X¹ represents an oxygen atom and m         represents 1 when X² represents an oxygen atom;     -   n represents 2 when X¹ represents a nitrogen atom and m         represents 2 when X² represents a nitrogen atom;     -   R¹ represents a linear or branched, saturated or unsaturated         alkyl group comprising from 3 to 30 carbon atoms, preferably         from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon         atoms;     -   R² represents a linear or branched, saturated or unsaturated         alkyl group comprising from 3 to 30 carbon atoms, preferably         from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon         atoms.     -   a mixture of at least one compound of formula (A) and at least         one compound of formula (B).

In another embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising at least one compound of formula (A1)

in which R¹ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms.

In another embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising a compound of formula (A1) in which R¹ represents an alkyl group comprising 11 carbon atoms.

In another embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising at least one compound of formula (A2)

in which R¹ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms.

In another embodiment of the invention, the organomolybdenum compound is a Mo-DTP compound comprising:

-   -   from 1 to 40%, preferably from 2 to 30%, more preferably from 3         to 28%, still more preferably from 4 to 15%, advantageously from         5 to 12 wt.-% of molybdenum, relative to the total weight of the         Mo-DTP compound;     -   from 1 to 40%, preferably from 2 to 30%, more preferably from 3         to 28%, even more preferentially from 4 to 15 wt.-% of sulfur,         relative to the total weight of the Mo-DTP compound;     -   from 1 to 10%, preferably from 2 to 8%, more preferably from 3         to 6 wt.-% of phosphorus, relative to the total weight of the         total weight of the Mo-DTP compound.

In another embodiment of the invention, the Mo-DTP compound is selected from among dimeric Mo-DTP compounds or trimeric Mo-DTP compounds.

In another embodiment of the invention, the Mo-DTP compound is a dimeric Mo-DTP compound of formula (C)

-   -   in which     -   R3, R4, R9 and R10, which are identical or different,         independently represent a hydrocarbon group chosen from alkyl,         alkenyl, aryl, cycloalkyl or cycloalkenyl groups,     -   R5, R6, R7 and R8, which are identical or different,         independently represent an oxygen atom or a sulfur atom.

In another embodiment of the invention, the Mo-DTP compound is a dimeric Mo-DTP compound of formula (C1)

in which R3, R4, R9 and R10, which are identical or different, independently represent a hydrocarbon group chosen from among alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl groups, preferably an alkyl group comprising from 4 to 12 carbon atoms, advantageously from 6 to at 10 carbon atoms.

In another embodiment of the invention, the compound Mo-DTP is a dimeric Mo-DTP compound of formula (C1) in which R3, R4, R9 and R10, which are identical, represent a C8-alkyl group, preferably an ethylhexyl group.

In another embodiment of the invention, the content by weight of organomolybdenum compound, relative to the total weight of the lubricating composition, ranges from 0.05 to 3%, preferably from 0.1 to 2%, advantageously from 0.1 to 1%.

In another embodiment of the invention, the lubricating composition further comprises an additional additive chosen from among friction modifiers with the exception of Mo-DTP compounds and sulfur-free molybdenum complexes, detergents, anti-doping and anti-wear additives, extreme pressure additives, viscosity index improvers, dispersants, antioxidants, pour point improvers, defoamers, thickeners and mixtures thereof.

In another embodiment of the invention, the lubricating composition is used to prevent or reduce pre-ignition in a vehicle engine, preferably of a motor vehicle.

In another embodiment of the invention, the lubricating composition is used to prevent or reduce low speed pre-ignition (LSPI) in an engine preferably of a vehicle, preferably of a motor vehicle.

The invention also relates to a method for preventing or reducing pre-ignition in an engine, wherein the method comprises at least one step of contacting a mechanical part of the engine with a lubricating composition as defined above.

The invention also relates to the use of an organomolybdenum compound in a lubricating composition comprising at least one base oil for preventing or reducing pre-ignition in an engine, wherein the organomolybdenum compound is chosen from among:

-   -   molybdenum dithiophosphate compounds (Mo-DTP), or     -   molybdenum complexes free from sulfur.

DETAILED DESCRIPTION OF THE INVENTION

The percentages given below correspond to percentages by weight of active ingredient.

The lubricating composition used according to the invention comprises at least one organomolybdenum compound chosen from among:

-   -   molybdenum dithiophosphate compounds (Mo-DTP), or     -   molybdenum complexes free from sulfur.

Molybdenum Complex Free from Sulfur

In one embodiment of the invention, the organomolybdenum compound may be chosen from among sulfur-free molybdenum complexes such as carboxylates, esters or molybdenum amides, obtainable by reaction of molybdenum oxide or molybdates of ammonium with fatty substances, glycerides, fatty acids or fatty acid derivatives (esters, amines, amides . . . ).

In a preferred embodiment of the invention, the organomolybdenum compound is selected from among sulfur-free molybdenum complexes with amide ligands, mainly prepared by reaction of a molybdenum source, which may be, for example, molybdenum, and an amine derivative, and fatty acids preferably comprising from 4 to 28 carbon atoms, more preferably from 8 to 18 carbon atoms, such as, for example, the fatty acids contained in vegetable or animal oils.

The synthesis of such compounds is described, for example, in U.S. Pat. No. 4,889,547, EP 0546357, U.S. Pat. No. 5,412,130 and EP 1770153.

In a preferred embodiment of the invention, the organomolybdenum compound is chosen from among sulfur-free molybdenum complexes obtained by reaction:

-   -   (i) a mono-, di- or tri-glyceride-type fatty substance, or fatty         acid,     -   (ii) an amino source of formula (D):

-   -   in which:         -   X¹ represents an oxygen atom or a nitrogen atom,         -   X² represents an oxygen atom or a nitrogen atom,         -   n and m represent 1 when X¹ or X² represent an oxygen atom,         -   n and m represent 2 when X¹ or X² represent a nitrogen atom,     -   (iii) and a molybdenum source selected from among molybdenum         trioxide or molybdates, preferably ammonium molybdate, in an         amount sufficient to provide 0.1 to 30% molybdenum based on the         total weight of complex.

In one embodiment of the invention, the sulfur-free molybdenum complex may comprise from 2 to 8.5% by weight of molybdenum based on the weight of complex.

In a preferred embodiment of the invention, the molybdenum sulfur complex comprises at least one compound selected from among:

-   -   the compounds of formula (A)

-   -   in which:     -   X¹ represents an oxygen atom or a nitrogen atom;     -   X² represents an oxygen atom or a nitrogen atom;     -   n represents 1 when X¹ represents an oxygen atom and m         represents 1 when X² represents an oxygen atom;     -   n represents 2 when X¹ represents a nitrogen atom and m         represents 2 when X² represents a nitrogen atom;     -   R¹ represents a linear or branched, saturated or unsaturated         alkyl group comprising from 3 to 30 carbon atoms, preferably         from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon         atoms;     -   the compounds of formula (B)

-   -   in which:     -   X¹ represents an oxygen atom or a nitrogen atom;     -   X² represents an oxygen atom or a nitrogen atom;     -   n represents 1 when X¹ represents an oxygen atom and m         represents 1 when X² represents an oxygen atom;     -   n represents 2 when X¹ represents a nitrogen atom and m         represents 2 when X² represents a nitrogen atom;     -   R¹ represents a linear or branched, saturated or unsaturated         alkyl group comprising from 3 to 30 carbon atoms, preferably         from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon         atoms;     -   R² represents a linear or branched, saturated or unsaturated         alkyl group comprising from 3 to 30 carbon atoms, preferably         from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon         atoms.     -   a mixture of at least one compound of formula (A) and at least         one compound of formula (B).

In one embodiment of the invention, the sulfur-free molybdenum complex is prepared by reacting:

-   -   (i) a mono-, di- or tri-glyceride-type fatty substance, or fatty         acid,     -   (ii) a diethanolamine or 2- (2-aminoethyl) aminoethanol,     -   (iii) and a molybdenum source selected from among molybdenum         trioxide or molybdates, preferably ammonium molybdate, in an         amount sufficient to provide 0.1 to 20.0% molybdenum based on         the weight of the complex.

In a preferred embodiment of the invention, the molybdenum sulfur complex comprises at least one compound of formula (A1) or a compound of formula (A2), taken alone or as a mixture:

in which R¹ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms,

in which R¹ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms.

Advantageously, the organomolybdenum compound is a sulfur-free molybdenum complex comprising a compound of formula (A1) in which R¹ represents an alkyl group comprising 11 carbon atoms.

Examples of sulfur-free molybdenum complexes include Molyvan 855 marketed by R.T Vanderbilt Company.

Molybdenum Dithiophosphate Compound (Mo-DTP)

The molybdenum dithiophosphate (Mo-DTP) compounds are complexes formed by a metal ring bonded to one or more ligands, wherein the ligand is an alkyl dithiophosphate group.

In one embodiment, the Mo-DTP compound used in the lubricating compositions according to the invention may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, even more preferably from 4 to 15%, advantageously from 5 to 12% by weight of molybdenum, relative to the total weight of Mo-DTP compound.

In one embodiment, the Mo-DTP compound used in the lubricating compositions according to the invention may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, even more preferably from 4 to 15% by weight of sulfur, relative to the total weight of Mo-DTP compound.

In one embodiment, the Mo-DTP compound used in the lubricating compositions according to the invention may comprise from 1 to 10%, preferably from 2 to 8%, more preferably from 3 to 6% by weight of phosphorus, relative to the total weight of the total weight of the Mo-DTP compound.

The Mo-DTP compound used in the lubricating compositions according to the invention may be chosen from compounds whose structure comprises two molybdenum atoms (also called dimeric Mo-DTP) and compounds whose structure comprises three molybdenum atoms (also called trimeric Mo-DTP).

The trimeric Mo-DTP compound has the following formula Mo₃S_(k)L_(n) in which:

-   -   k represents an integer at least equal to 4, preferably from 4         to 10, advantageously from 4 to 7,     -   n represents an integer ranging from 1 to 4, and     -   L represents an alkyl dithiophosphate group comprising from 1 to         100 carbon atoms, preferably from 1 to 40 carbon atoms,         advantageously from 3 to 20 carbon atoms.

Examples of Mo-DTP-trimer compounds according to the invention include compounds and methods for their preparation as described in WO98/26030 and US2003/022954.

Advantageously, the Mo-DTP compound used in the context of the invention is a dimeric Mo-DTP compound.

Examples of dimeric Mo-DTP compounds include the compounds as described in EP0757093 or EP0743354.

Dimeric Mo-DTP generally corresponds to the compounds of formula (C):

-   -   in which:     -   R3, R4, R9 and R10, which may be identical or different,         independently represent a hydrocarbon group chosen from alkyl,         alkenyl, aryl, cycloalkyl or cycloalkenyl groups,     -   R5, R6, R7 and R8, which may be identical or different,         independently represent an oxygen atom or a sulfur atom.

In one embodiment, R3, R4, R9 and R10, which may be identical or different, independently represent an alkyl group comprising from 4 to 18 carbon atoms or an alkenyl group comprising from 2 to 24 carbon atoms.

In one embodiment, R5, R6, R7 and R8 may be identical and may represent a sulfur atom.

In another embodiment, R5, R6, R7 and R8 may be identical and may represent an oxygen atom.

In another embodiment, R5 and R6 may represent a sulfur atom, while R7 and R8 may represent an oxygen atom.

In another embodiment, R5 and R6 may represent an oxygen atom, while R7 and R8 may represent a sulfur atom.

In a preferred embodiment of the invention, the compound Mo-DTP is chosen from among compounds of formula (C) in which:

-   -   R5 and R6 represent an oxygen atom,     -   R7 and R8 represent a sulfur atom,     -   R3 represents an alkyl group comprising from 4 to 12 carbon         atoms, preferably from 6 to 10 carbon atoms,     -   R4 represents an alkyl group comprising from 4 to 12 carbon         atoms, preferably from 6 to 10 carbon atoms,     -   R9 represents an alkyl group comprising from 4 to 12 carbon         atoms, preferably from 6 to 10 carbon atoms,     -   R10 represents an alkyl group comprising from 4 to 12 carbon         atoms, preferably from 6 to 10 carbon atoms.

Advantageously, the Mo-DTP compound is chosen from among compounds of formula (C) in which:

-   -   R5 and R6 represent an oxygen atom,     -   R7 and R8 represent a sulfur atom,     -   R3 represents an ethylhexyl group,     -   R4 represents an ethylhexyl group,     -   R9 represents an ethylhexyl group,     -   R10 represents an ethylhexyl group.

Advantageously, the compound Mo-DTP is chosen from compounds of formula (C1)

-   -   in which R3, R4, R9 and R10 are as defined for formula (C).

Advantageously, the compound Mo-DTP is chosen from among compounds of formula (C1) in which R3, R4, R9 and R10, which are identical or different, independently represent a hydrocarbon group chosen from alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl, preferably an alkyl group comprising from 4 to 12 carbon atoms, preferably from 6 to 10 carbon atoms.

Even more advantageously, the compound Mo-DTP is chosen from among compounds of formula (C1) in which R3, R4, R9 and R10 represent a C8-alkyl group, preferably an ethylhexyl group.

As examples of Mo-DTP compounds, mention may be made of the Molyvan L product marketed by the company R.T Vanderbilt Company or the Sakuralube 300 or Sakuralube 310G products sold by the company Adeka.

In one embodiment of the invention, the content by weight of organomolybdenum compound, relative to the total weight of the lubricating composition, ranges from 0.05 to 3%, preferably from 0.1 to 2%, advantageously from 0.1 to 1%.

The lubricating composition used according to the invention also comprises at least one base oil.

In general, the lubricating composition used according to the invention may comprise any type of mineral, synthetic or natural, animal or vegetable, lubricating base oil known to persons skilled in the art.

The base oils used in the lubricating compositions according to the invention may be oils of mineral or synthetic origins belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (Table A), or their mixtures.

TABLE A Saturated Sulfur Viscosity index content content (VI) Group I Mineral oils <90% >0.03% 80 ≤ VI < 120 Group II Hydrocracked ≥90% ≤0.03% 80 ≤ VI < 120 oils Group III Hydrocracked ≥90% ≤0.03% ≥120 or hydro-isomerized oils Group IV Polyalphaolefines (PAO) Polyalphaolefines (PAO) Group V Esters and other bases not included in groups I to IV

The mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalting, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

Mixtures of synthetic and mineral oils may also be used.

There is generally no limitation on the use of different lubricating bases for producing the lubricating compositions used according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulfur, oxidation resistance, that are suitable for use for engines or for vehicle transmissions.

The base oils of the lubricating compositions used according to the invention may also be chosen from synthetic oils, such as certain carboxylic acid esters and alcohols, and from polyalphaolefins. The polyalphaolefins used as base oils are, for example, obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100° C. is between 1.5 and 15 mm².s⁻¹ according to ASTM D445. Their average molecular weight is generally between 250 and 3000 according to ASTM D5296.

Preferably, the base oils of the present invention are chosen from the above base oils whose aromatic content is between 0 and 45%, preferably between 0 and 30%. The aromatic content of the oils is measured according to the Burdett UV method.

Advantageously, the lubricating composition used according to the invention comprises at least 50% by weight of base oils relative to the total weight of the composition.

More advantageously, the lubricating composition used according to the invention comprises at least 60% by weight, or even at least 70% by weight, of base oils relative to the total weight of the composition.

More particularly advantageously, the lubricating composition used according to the invention comprises from 60 to 99.5% by weight of base oils, preferably from 70 to 99.5% by weight of base oils, relative to the total weight of the composition.

Many additives may be used for this lubricating composition used according to the invention.

The preferred additives for the lubricating composition used according to the invention are chosen from among friction modifiers with the exception of Mo-DTP compounds and sulfur-free molybdenum complexes, detergents, anti-wear additives, extreme pressure additives, viscosity index improvers, dispersants, antioxidants, pour point improvers, defoamers, thickeners and mixtures thereof.

Preferably, the lubricating composition used according to the invention comprises at least one anti-wear additive, and at least one extreme pressure additive or their mixtures.

The anti-wear additives and extreme pressure additives protect the friction surfaces by forming a protective film adsorbed on these surfaces.

There is a wide variety of anti-wear additives. In a preferred manner for the lubricating composition according to the invention, wherein the anti-wear additives are chosen from among phospho-sulfur-containing additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTPs. The preferred compounds have the formula Zn((SP(S)(OR¹¹)(OR¹²))₂, in which R¹¹ and R¹², which may be identical or different, independently represent an alkyl group, preferably an alkyl group comprising from 1 to 18 carbon atoms.

Amine phosphates are also anti-wear additives that may be used in the lubricating composition according to the invention. However, the phosphorus provided by these additives may act as a poison of the catalytic systems of automobiles because these additives are ash generators. These effects may be minimized by partially substituting the amine phosphates with non-phosphorus additives, such as, for example, polysulfides, especially sulfur-containing olefins. Advantageously, the lubricating composition according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight relative to the total weight of lubricating composition, anti-wear additives and extreme pressure additives.

Advantageously, the lubricating composition according to the invention may comprise at least one additional friction-modifying additive with the exception of Mo-DTP compounds and sulfur-free molybdenum complexes. The additional friction modifier additive may be selected from a compound providing metal elements and an ash free compound. Among the compounds providing metal elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu and Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus. The ashless friction modifier additives are generally of organic origin and may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides, fatty amines or fatty acid glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

Advantageously, the lubricating composition according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or 0.1 at 2% by weight relative to the total weight of the lubricating composition, anti-wear and extreme pressure additives.

Advantageously, the lubricating composition according to the invention may comprise at least one antioxidant additive.

The antioxidant additive generally serves to delay the degradation of the lubricating composition in use. This degradation may notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricating composition.

Antioxidant additives act in particular as radical inhibitors or destroyers of hydroperoxides. Among the antioxidant additives commonly used, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type, antioxidant phosphosulfur additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, may be ash generators. Phenolic antioxidant additives may be ash-free or may be in the form of neutral or basic metal salts. The antioxidant additives may especially be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C₁-C₁₂ alkyl group, and N, N′-dialkyl-aryl diamines and mixtures thereof.

Preferably, according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon bearing the alcohol function is substituted by at least one C₁-C₁₀ alkyl group, preferably a C₁-C₆ alkyl group, preferably a C₄ alkyl group, preferably by the ter-butyl group.

Amino compounds are another class of antioxidant additives that may be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR¹³R¹⁴R¹⁵ in which R¹³ represents an optionally substituted aliphatic or aromatic group, R¹⁴ represents an optionally substituted aromatic group, R¹⁵ represents a hydrogen atom, a alkyl group, an aryl group or a group of the formula R¹⁶S(O)₂R¹⁷ wherein R¹⁶ represents an alkylene group or an alkenylene group, R¹⁷ represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulfurized alkyl phenols or their alkali and alkaline earth metal salts may also be used as antioxidant additives.

Another class of antioxidant additives is copper compounds, for example copper thio- or dithio-phosphates, copper and carboxylic acid salts, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper salts I and II, succinic acid or anhydride salts, may also be used.

The lubricating composition according to the invention may contain all types of antioxidant additives known to persons skilled in the art.

Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive.

Also advantageously, the lubricating composition according to the invention comprises from 0.5 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive.

The lubricating composition according to the invention may also comprise at least one detergent additive.

The detergent additives generally make it possible to reduce the formation of deposits on the surface of the metal parts by dissolving the secondary oxidation and combustion products.

The detergent additives that may be used in the lubricating composition according to the invention are generally known to persons skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or alkaline earth metal.

The detergent additives are preferably chosen from the alkali metal or alkaline earth metal salts of carboxylic acids, the sulphonates, the salicylates, the naphthenates and the phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

These metal salts generally comprise the metal in stoichiometric amount or in excess, therefore in an amount greater than the stoichiometric amount. It then relates to overbased detergent additives; the excess metal bringing the overbased character to the detergent additive is then generally in the form of an oil insoluble metal salt, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate.

Advantageously, the lubricating composition according to the invention may comprise from 2 to 4% by weight of detergent additive relative to the total weight of the lubricating composition.

Also advantageously, the lubricating composition according to the invention may also comprise at least one pour point depressant additive.

By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricating composition according to the invention.

As examples of pour point depressant additives, mention may be made of alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes.

Advantageously, the lubricating composition according to the invention may also comprise at least one dispersing agent.

The dispersing agent may be chosen from among Mannich bases, succinimides and their derivatives.

Also advantageously, the lubricating composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent relative to the total weight of the lubricating composition.

The lubricating composition of the present invention may also comprise at least one additive improving the viscosity index. Examples of additives which improve the viscosity index include polymeric esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, of styrene, butadiene and isoprene, in particular polyacrylates, polymethacrylates (PMA) or olefin copolymers, especially ethylene/propylene copolymers.

The lubricating composition according to the invention may be in various forms. The lubricating composition according to the invention may, in particular, be an anhydrous composition.

Preferably, this lubricating composition is not an emulsion.

The lubricating composition defined above is used to prevent or reduce pre-ignition in an engine.

By engine according to the invention, is meant more particularly vehicle engines, such as:

-   -   motor vehicle engines, including petrol and diesel engines, but         also gas and petrol engines (dual fuel gas/gasoline engines) and         gas and diesel engines (dual fuel gas/diesel engines);     -   the engines of heavy goods vehicles, and more specifically the         engines of heavy goods vehicles running on gas.

By engine according to the invention is also meant 4-stroke engines, and more specifically 4-stroke marine engines, preferably 4-stroke marine engines operating on gas.

In a preferred embodiment of the invention, the lubricating composition is used to prevent or reduce pre-ignition in a vehicle engine, preferably a motor vehicle.

Pre-ignition according to the invention includes the phenomenon of low frequency vibration producing a rumble sound effect. By pre-ignition according to the invention is more particularly meant low-speed pre-ignition (LSPI).

In a preferred embodiment of the invention, the lubricating composition is used to prevent or reduce low speed pre-ignition (LSPI) in an engine, preferably in a vehicle engine, preferably a motor vehicle.

The invention also relates to a method for preventing or reducing pre-ignition in an engine, wherein the method comprises at least one step of contacting a mechanical part of the engine with a lubricating composition as defined above.

All of the features and preferences described for the above use also apply to this method.

The invention also has the use of an organomolybdenum compound in a lubricating composition comprising at least one base oil for preventing or reducing pre-ignition in an engine, wherein the organomolybdenum compound is chosen from:

-   -   molybdenum dithiophosphate compounds (Mo-DTP), or     -   molybdenum complexes free from sulfur.

The set of characteristics and preferences relating to the organomolybdenum compound and the lubricating composition described above also apply to this use.

The various aspects of the invention may be illustrated by the following examples:

EXAMPLE 1 Preparation of Lubricating Compositions According to the Invention

The various components of the lubricating compositions according to the invention Cl1 and Cl2 are mixed according to the nature and the quantities presented in Table 1.

TABLE 1 Cl1 Cl2 Gr III base oil 85.01 84.77 Viscosity Index Improver 5.00 5.00 (Polyisobutene Styrene Hydrogenated or PISH) Anti-wear (DTPZn) 0.63 0.80 Antioxidant amine (Diphenylamine) 0.80 0.80 Detergent (Calcium sulphonate) 2.00 2.00 Dispersant (Bis-Succinimide) 6.00 6.00 Mo-DTP (Sakuralube 300) 0.56 Sulfur-Free Molybdenum Complex 0.63 (Molyvan 855) KV 100 (measured in mm²/s 8.3 8.3 according to ASTM D445)

EXAMPLE 2 Preparation of Comparative Lubricating Compositions

The various components of the comparative lubricating composition CC1 are mixed according to the nature and amounts shown in Table 2

TABLE 2 CC1 Gr III base oil 84.90 Viscosity Index Improver 5.00 (Polyisobutene Styrene Hydrogenated or PISH) Anti-wear (DTPZn) 0.80 Antioxidant amine (Diphenylamine) 0.80 Detergent (Calcium sulphonate) 2.00 Dispersant (Bis-succinimide) 6.00 Mo-DTC (Sakuralube 525) 0.50 KV 100 (measured in mm²/s 8.3 according to ASTM D445)

EXAMPLE 3 Evaluation of the Pre-Ignition Reduction Properties of the Lubricating Compositions according to the invention Cl1 and Cl2 and of the comparative lubricating composition CC1

This evaluation is performed by evaluating the impact of each lubricating composition on the low-speed pre-ignition (LSPI).

For this, the LSPI phenomenon is quantified by means of a GM Ecotech model spark ignition turbocharged engine composed of 4 cylinders in line for a total displacement of 2.0 L.

After a heating period of 20 minutes at an engine speed of 2000 rpm and an engine load of 4.10⁵ Pascal effective average pressure (EAP), the test procedure consists of 2 sequences under heavy load (23.10⁵ Pascal EAP at a speed of 2.000 rpm), 2 sequences under low load (13.10⁵ Pascal of EAP at a speed of 1.250 rpm) and 2 sequences under heavy load identical to the first 2. Each sequence comprises 25.000 motor cycles to ensure a good statistical representativeness of the phenomenon studied.

Each cylinder is equipped with a sensor to measure the pressure in the combustion chamber during engine operation. A high frequency recorder records the pressure signal allowing a fine analysis of the combustion. A combustion is considered an LSPI event if one of the following 2 criteria is fulfilled:

-   -   the maximum pressure of a cycle is greater than the average of         the maximum pressures on the whole sequence considered +4.7         times the standard deviation of maximum pressure measured on the         sequence;     -   the crankshaft angle at which 2% of the fuel mixture mass burned         on a given cycle is less than the average of the crankshaft         angles at which 2% of the mass of fuel mixture burned over the         entire sequence considered plus 4.7 times the standard deviation         on the crankshaft angle at which 2% of the mass of combustible         mixture burned on all the frequency.

The sum of the LSPI events is counted on all 6 sequences of the procedure for a given lubricating composition. This test is repeated 4 times for each lubricated composition tested.

The impact of the lubricating composition on the LSPI is compared by comparing the average of the number of LSPI events on the four engine tests and taking into account the standard deviation calculated on the four engine tests.

The results concerning the lubricating compositions according to the invention Cl1 and Cl2 and the comparative lubricating composition CC1 are given in Table 3; the lower the number of LSPI events, the better the performance of the lubricating composition to prevent or reduce pre-ignition.

TABLE 3 Cl1 Cl2 CC1 Number of LSPI 193 229 324 events

The results show that the lubricating compositions according to the invention comprising respectively an Mo-DTP (composition Cl1) and a sulfur-free molybdenum complex (composition Cl2) exhibit improved LSPI reduction properties compared to a lubricating composition comprising a molybdenum dithiocarbamate organomolybdenum (Mo-DTC) compound. 

1-11. (canceled)
 12. Method of prevention or reduction of pre-ignition in a vehicle engine, wherein the method comprises at least one step of contacting a mechanical part of the engine with a lubricating composition comprising at least one base oil and at least one organomolybdenum compound wherein the organomolybdenum compound is selected from among sulfur-free molybdenum complexes.
 13. Method according to claim 12, wherein the organomolybdenum compound is a sulfur-free molybdenum complex selected from among organic complexes of molybdenum with ligands of amide type and prepared via reaction of a molybdenum source, an amine derivative and fatty acids.
 14. Method according to claim 12, wherein the organomolybdenum compound is a sulfur-free molybdenum complex and comprising at least one compound selected from among: compounds of formula (A):

where: X¹ is an oxygen atom or nitrogen atom; X² is an oxygen atom or nitrogen atom; n is 1 when X¹ is an oxygen atom and m is 1 when X² is an oxygen atom; n is 2 when X¹ is a nitrogen atom and m is 2 when X² is a nitrogen atom; R₁ is an alkyl group, linear or branched, saturated or unsaturated, comprising from 3 to 30 carbon atoms; compounds of formula (B)

where: X¹ is an oxygen atom or nitrogen atom; X² is an oxygen atom or nitrogen atom; n is 1 when X¹ is an oxygen atom and m is 1 when X² is an oxygen atom; n is 2 when X¹ is a nitrogen atom and m is 2 when X² is a nitrogen atom; R₁ is a an alkyl group, linear or branched, saturated or unsaturated, comprising from 3 to 30 carbon atoms; R₂ is an alkyl group, linear or branched, saturated or unsaturated, comprising from 3 to 30 carbon atoms, a mixture of at least one compound of formula (A) and at least one compound of formula (B).
 15. Method according to claim 12, wherein the organomolybdenum compound is a sulfur-free molybdenum complex and comprising at least one compound of formula (A1):

where R₁ is an alkyl group, linear or branched, saturated or unsaturated, comprising from 3 to 30 carbon atoms.
 16. Method according to claim 15, wherein the organomolybdenum compound is a sulfur-free molybdenum complex and comprising a compound of formula (A1) where R₁ is an alkyl group comprising 11 carbon atoms.
 17. Method according to claim 12, wherein the organomolybdenum compound is a sulfur-free molybdenum complex and comprising at least one compound of formula (A2)

where R1 is a alkyl group, linear or branched, saturated or unsaturated, comprising from 3 to 30 carbon atoms.
 18. Method according to claim 12, wherein the weight content of organomolybdenum compound relative to the total weight of the lubricating composition ranges from 0.05 to 3%.
 19. Method according to claim 12, wherein the lubricating composition further comprises an additional additive selected from among friction modifiers with the exception of sulfur-free molybdenum complexes, detergents, anti-wear additives, extreme pressure additives, viscosity index improvers, dispersants, antioxidants, pour point depressants, defoamers, thickeners and mixtures thereof.
 20. Method according to claim 12 to prevent or reduce pre-ignition in a motor vehicle.
 21. Method according to claim 12 to prevent or reduce Low Speed Pre-Ignition (LSPI) in an engine. 